The US is sending in the ­cavalry to fight the crisis in the credit and housing markets – unleashing government-sponsored enterprises to buy and hold mortgage-backed securities (MBS) for which there is little private demand.

The move marks a new stage in the policy response to the credit crisis, in which the US government is increasingly deploying all the tools at its disposal – short of an outright public purchase of mortgage securities – to prevent a full-blown credit crunch.